In patients with heart failure, there is a need for therapeutically enhancing blood flow using an implantable system. Cardiac support systems include, but are not limited to, left ventricular assist devices (LVADs), right ventricular assist devices (RVADs), using two devices to assist both ventricles as a bi-ventricular assist device (BiVADs), and total artificial hearts (TAHs). Ventricular assist devices (VADs) that are suitable for adults may call for approximately 5 liters/min (LPM) of blood flow at 100 mm of Hg differential pressure which equates to about 1 watt of hydraulic power. Currently available implantable continuous flow blood pumps consume significantly more electric power to produce the desired amount of flow and pressure.
High pump power consumption of current systems may make it impractical to implant a power source of sufficient capacity for a full day of awake hours of operation in the body. For example, size restrictions of implantable power sources may only allow the implantable power source to provide up to an hour of operation time. Instead, high power consumption blood pumps may provide a wire connected to the pump that exits the body (i.e. percutaneous) for connection to a power source that is significantly larger than an implantable power source. These blood pumps may require external power to be provided at all times to operate. In order to provide some mobility, external bulky batteries and controllers may be utilized. However, percutaneous wires and externally worn components can still restrict the mobility of a person with such a blood pump implant. For example, such high power consumption blood pumps have external batteries that frequently require recharging thereby limiting the amount of time the person can be away from a charger or power source, external batteries and controllers that can be heavy or burdensome thereby restricting mobility, percutaneous wire skin penetrations that are not suitable for prolonged exposure to water submersion (i.e. swimming, bathing, etc.), and/or other additional drawbacks.
For example, negative impacts of these types of systems may include susceptibility to infection, constraints on sleep position, restrictions on water activities such as swimming and bathing, concern for wire entanglement or severing, necessity to avoid static discharges, and a multitude of others. Furthermore, the external batteries and control systems are burdensome. It would be advantageous to eliminate the percutaneous wire and burdensome external batteries and control system.
While there is limited use of wireless power systems in some neural stimulators, widespread use of wireless power systems for implantable heart pumps has not been adopted. Currently, few applications of wireless power transfer have been applied to VADs or TAHs due to the higher power transfer levels required, relatively high power consumption of such devices, limited space available for implantable rechargeable batteries, limited capacity of implantable rechargeable batteries, and the like.
However, in order to overcome issues associated with percutaneous wires, some wireless power transfer systems have been developed that use inductive coupling between an implanted coil and an external coil to transfer power across the skin, thereby obviating the need for a percutaneous wire. This type of wireless power transfer system simply uses the inductive effect between two coils similar to a standard transformer. This approach has been used widely to recharge implanted batteries in some neural stimulators. Further, these inductive systems may require precise alignment between the two coils, and may require close spacing between coils on the order of a few inches or less. These inductive systems can generate significant amounts of heat near the skin, and require the patient to be immobile during charging if the external power source is not easily mobile. Energy lost by such systems is generally released as heat that is dissipated into the human body, which may produce heat-related health complications or require additional components to compensate for the heat generated.
LionHeart LVD-2000 LVAD from Arrow International, Inc. and the HeartSaver™ LVAD from WorldHeart Corporation eliminated the percutaneous wire by powering the implanted portion using inductively-coupled Transcutaneous Energy Transfer (TET). These systems eliminated the wire, but did not eliminate the burdensome external batteries and control system which still had to be worn by the patient. For example, the LionHeart LVD-2000 had a rechargeable implantable battery for brief periods when the external power was unavailable or needed to be removed. However, due to the energy demands of the implanted system, that implantable battery could supply only about 20 minutes of energy. Note that the size of an acceptable system for implanting into a patient constrains the capacity of implantable energy storage. Consequently, although the LionHeart LVD-2000 did not require a percutaneous wire, the burden of the external batteries and controller remained similar to that of systems with a percutaneous wire.
Implantable cardiac support systems have numerous sources of potential energy inefficiency. To produce a therapeutically enhanced blood flow, power is needed to produce a particular desired blood flow rate at a particular desired pressure. Blood flow may be imparted by an electro-mechanical device, such as by a rotary pump. The design of the electro-mechanical device is critical to efficiently transferring the electrical energy powering the device into the desired blood flow. Further, a cardiac support system may also include an energy storage system. The design and operation of the energy storage system is critical to efficiently maintain and transfer stored electrical energy.
As a result of the significant drawbacks of existing systems, there is an unmet need for an energy-efficient cardiac support system capable of eliminating percutaneous wires for power or control, and doing so without burdening the patient with external batteries or controllers. There is an unmet need for a system which not only restores cardiac function, but restores an unburdened ambulatory lifestyle.